用Response导出excel表。图片无法显示。怎么办？

Question

用Response导出excel表，有图片和标题，datagrid。除了图片都能正常导出显示。图片就变成叉叉。
代码如下：  
            Response.Clear();
　　        Response.Buffer= true;
　　        Response.Charset="GB2312";
Response.AppendHeader("Content-Disposition","attachment;filename=FileFlow.xls");
　　        Response.ContentEncoding=System.Text.Encoding.GetEncoding("GB2312");
　　        Response.ContentType = "application/vnd.ms-excel";
　　
  //　定义一个输入流
　　        System.IO.StringWriter oStringWriter = new System.IO.StringWriter();
　       　 System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);
            this.ClearControls(DataGrid1);
   this.header.RenderControl(oHtmlTextWriter);
            this.DataGrid1.RenderControl(oHtmlTextWriter);
   this.foot.RenderControl(oHtmlTextWriter);
　     　　 Response.Write(oStringWriter.ToString());
　　        Response.End();